An ash plume rising from the Overlook crater.Photo: Courtesy of U.S. Geological Survey

When volcanoes ooze lava, people know to get the hell out of the way. They know the fiery red stuff threatens their homes and lives. But what about when eruptions produce lots of ash and gas? That stuff can be deadly, too.

The Kilauea volcano in Pahoa, Hawaii, has been going off since earlier this month. Before Tuesday, residents and visitors to the Big Island had to be wary of the lava oozing out of fissures, which destroyed at least 26 homes. Now, they’ve also gotta worry about the ash flying out of the volcano’s summit crater 12,000 feet into the air, which is scary in a different way.

You see, this isn’t the same ash that flies out of your fireplace when you’re trying to warm up in the winter. “Ash is not fluffy,” said Janine Krippner, a volcanologist at Concord University, to Earther. “It’s actually ground up pulverized rock, crystal, and glass, so it’s very sharp.”

You definitely don’t want to get this stuff in your eyes, Krippner said. (She speaks from experience.) But this ash is also dangerous to inhale. After all, volcanic ash, like the particulate matter from power plants and vehicle pollutants, can lodge itself deep in a person’s lungs.

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“We have more control over these other emissions, but they’re the same kind of pollutants we see from this naturally occurring source,” said Janice Nolen, the assistant vice president of national policy at the American Lung Association, to Earther.

Activity at Halema‘uma‘u crater upgraded to ashfall on May 15, 2018.Photo: Courtesy of U.S. Geological Survey

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Industrial pollution is often pretty toxic. Volcanic ash, on the other hand, isn’t—not without the gases, at least, more on those in a moment. So while inhaling a ton of this ash is unlikely to cause cancer, it could lead to lung and heart disease. That would take some serious exposure, though. Slight exposure would trigger some nose and throat irritation, as well as difficulty breathing. However, folks who already suffer from respiratory issues like asthma (or more vulnerable groups like children and the elderly) can exhibit more extreme symptoms with any exposure, and should really steer clear of this muck.

What is toxic duringeruptions are the gases released in lava and alongside volcanic ash. A key pollutant from the fissures that have been erupting on and off for weeks is sulfur dioxide, which can create vog, aka volcanic smog. Officials have noted “dangerously high” levels of sulfur dioxide at Kilauea, Krippner said. And as Nolen over at the American Lung Association explained, the vog that forms from this gas contains more particles dangerous to health. So it’s a double whammy.

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Yellow sulfur deposits appear on the crack margins of a fissure. Photo: Courtesy of U.S. Geological Survey

For the most part, the wind is blowing all these particles to the southwest, away from the rest of the islands up north. In Pahala, Hawaii, a town of just over 1,000, vog and ashfall have been reported. If the wind shifts direction, the eruption could pose a threat to even more people. And ash can stick around for a while. Krippner couldn’t say how long the ash from yesterday’s summit outburstswould linger—it really depends on wind, rain, and vegetation—but the ash from the world’s largest eruption of the 20th century in Alaska still remobilizes today, more than 100 years after it happened.

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Krippner doubts Hawaii will experience anything like that, but it’s a good reminder of how ash can stick around. Nolen worries about the impacts residents will face once all the chaos has passed and they start cleaning up. Moving around debris and cleaning out one’s home can stir up that residual ash. “We see this with hurricanes and wildfires, as well,” Nolen said.

The Big Island’s got some time before this volcano lets up. Kilauea’s lava lake could descend deeper inside the crater, beneath the water table. With that, more eruptions like we saw Tuesday could happen. At least now the community’s seen a preview.